I have a soft coral touching a leather coral and the leather tends to not open up as much where the touch. This could also be due to shading, but I haven't seen any aggression on the part of the soft or leather coral yet, as both are doing well. I think the soft coral is possibly a tree coral, but not sure. The leather is a devils hand leather (is that sarcophyton or lobophytum? never remember which is which).
Both being octocorallia (soft corals), neither has nematocysts to sting the other. They defend space by releasing noxious chemicals into the water, primarilly terpenoids.
They may irritate one another where they touch, but you won't get the same destructive stinging that you will with stony corals.